Camshaft phasers for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. A prior art vane-type phaser generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve (OCV), in accordance with an engine control module, to either the advance or retard chambers as required to meet current or anticipated engine operating conditions.
In a typical prior art vane-type cam phaser, a controllably variable locking pin is slidingly disposed in a bore in a rotor vane to permit rotational locking of the rotor to the stator (or sprocket wheel or pulley) under certain conditions of operation of the phaser and engine. In older prior art phasers, it is desired that the rotor be locked at an extreme of the rotor authority, typically at the full retard position. To assist in positioning the rotor, it is known to incorporate a mechanical stop for the rotor and a torsional bias spring acting between the rotor and the stator to urge the rotor against the stop at the desired position for locking.
In newer prior art phasers, it is desirable that the rotor be lockable to the stator at an intermediate position in an increased rotor range of rotational authority. A known problem in such phasers is that there is no mechanical means such as a stop to assist in positioning the rotor for locking in an intermediate position; thus, locking is not reliable, and an unacceptably high rate of locking failures may occur. This problem is addressed by the torsional bias spring invention disclosed in U.S. Pat. No. 7,363,897, issued Apr. 29, 2008.
A problem not addressed is that the torsion bias spring may generate an unwanted torque on the rotor about an axis orthogonal to the rotor axis, causing the rotor to become slightly cocked within the stator chamber before the phaser is installed onto the end of a camshaft during engine assembly. This cocking is permitted by necessary clearances between the rotor and the stator. Although relatively slight, such cocking can be large enough to prohibit entry of the camshaft into the rotor during engine assembly.
An additional problem more recently recognized is the fact that in many modern engines the camshaft is called upon to perform cyclic functions in addition to the opening and closing of combustion valves. For example, it is known to employ an additional camshaft lobe to positively drive a piston pump for supplying fuel to an engine fuel rail in a direct-injection engine. The additional torque load in the phase-retard direction can impede the function of the bias spring and also slow the response of the rotor in the advance direction beyond the rotary locking position at which point the bias spring no longer engages the rotor.
What is needed in the art is an improved vane-type camshaft phaser wherein the rotor may be reliably locked to the stator at an intermediate position in the range of authority, and wherein the rotor of an assembled phaser may be reliably entered onto the end of a camshaft during engine assembly, and wherein the additional torque load on the camshaft is compensated within the phaser over the full range of phaser authority.
It is a primary object of the present invention to improve the operational reliability of a camshaft phaser.